This invention relates to integrated circuit voltage regulators, and more particularly, to integrated circuit voltage regulators having current bleeder circuits.
Integrated circuits contain circuitry that is powered at a variety of power supply levels. In a typical scenario, an integrated circuit may contain core logic that is powered using a relatively low power supply voltage and peripheral input-output circuitry that operates at a relatively high power supply voltage. Additional circuit functions may require other power supply voltages.
One way to satisfy the need for multiple power supply voltages on an integrated circuit is to require system designers to supply suitable power supply voltages externally. This approach requires system designers to design circuit boards in which a number of power supply voltages are routed to the power supply pins of the integrated circuit.
It is generally desirable to minimize the number of power supply pins that are used in a given design. The quantity of pins available to supply an integrated circuit with power supply voltages is limited due to considerations such as circuit real estate consumption and device complexity. Although it would be convenient to be able to add a new power supply pin for each new power supply voltage that is needed on an integrated circuit, this is generally not feasible in practice.
One way to overcome the limited number of power supply voltages that are supplied externally to an integrated circuit involves generating power supply voltages using on-chip voltage regulator circuitry. By using an on-chip voltage regulator, it is possible to generate a new power supply voltage that would otherwise not be available.
Voltage regulator circuitry may also be used on an integrated circuit to regulate externally supplied power supply voltages. This helps to ensure that the circuitry on the integrated circuit will be powered at the appropriate voltage level, even if the voltage of the external supply deviates somewhat from its nominal level.
A conventional voltage regulator includes an operational amplifier, an n-channel metal-oxide-semiconductor (NMOS) field-effect transistor, and a resistor. The operational amplifier has a first input that receives a reference voltage, a second input, and an output. The NMOS transistor has a drain terminal that is connected to a positive power supply line, a gate terminal that is shorted to the output of the operational amplifier, and a source terminal that is shorted to the second input of the operational amplifier. The resistor has a first terminal that is connected to the source terminal of the NMOS transistor and second terminal that is connected to a ground power supply line. The source terminal of the NMOS transistor may serve as the output of the voltage regulator. Other on-chip circuitry may receive a regulator voltage from the output of the voltage regulator and may thereby draw a load current from the regulator voltage.
Arranged in this way, the operational amplifier and the NMOS pass transistor are connected in a negative feedback configuration. The resistor serves as a fixed leakage current path that ensures stability of this feedback loop across worst-case process, voltage, and temperature (PVT) variations (i.e., the resistor helps to increase extra phase margin for voltage regulator). The fixed leakage current path, however, is always active and can increase the overall power consumption of the voltage regulator by up to 10% or more.